Cannula configured to deliver test stimulation

ABSTRACT

The disclosure is directed to an implant tool and cannula used to facilitate the implantation of a medical device into a patient. The implant tool includes a housing that is held by a user and a needle attached to the housing. The cannula may be positioned over the needle and delivered to a target tissue within the patient. The cannula includes an electrode at a distal portion to deliver test stimulation to confirm the location of the target site or placement of the implant tool relative to the target site before removing the needle of the implant tool. In this manner, the cannula may be repositioned within the patient until the position of the implant tool and cannula relative to the target site is verified with the test stimulation.

TECHNICAL FIELD

The invention relates to medical devices and, more particularly, devicesfor implanting other medical devices.

BACKGROUND

Electrical stimulation systems may be used to deliver electricalstimulation therapy to patients to treat a variety of symptoms orconditions such as chronic pain, tremor, Parkinson's disease, multiplesclerosis, spinal cord injury, cerebral palsy, amyotrophic lateralsclerosis, dystonia, torticollis, epilepsy, pelvic floor disorders,gastroparesis, or obesity. The electrical stimulation system may also beused for muscle stimulation, such as for function electrical stimulationof muscles. An electrical stimulation system typically includes one ormore implantable medical leads coupled to an external or implantableelectrical stimulator.

The implantable medical lead may be percutaneously or surgicallyimplanted in a patient on a temporary or permanent basis such that atleast one stimulation electrode is positioned proximate to a targetstimulation site. The target stimulation site may be, for example, anerve or other tissue site, such as a spinal cord, pelvic nerve,pudendal nerve, sacral nerve, peripheral nerve, stomach, bladder, orwithin a brain or other organ of a patient, or within a muscle or musclegroup of a patient. The one or more electrodes located proximate to thetarget stimulation site may deliver electrical stimulation therapy tothe target stimulation site in the form of electrical signals.

SUMMARY

In general, the disclosure relates to an implant tool and a cannula thatmay be used to facilitate the implantation of a medical device into apatient. The implant tool includes a housing that is held by a user anda needle attached to the housing. The needle is configured so that thecannula may be positioned over the needle and delivered to the targettissue site by the needle. Once the needle is in place relative to atarget site within the patient, the needle is removed and a medicaldevice may be implanted through the lumen of the cannula that remainswithin the patient. In one embodiment, a distal end of the needle ispositioned proximate to the target site. The cannula includes anelectrode at the distal end of the cannula to deliver test stimulationto a target site before removing the needle of the implant tool. In thismanner, the cannula may be repositioned within the patient until thelocation of the implant tool and cannula relative to the target site isverified with the test stimulation. The cannula also includes anelectrical contact at the proximal end of the cannula that couples to asource of electrical stimulation. For example, in one embodiment, theelectrical contact at the proximal end of the cannula couples to anelectrical contact of the implant tool and a conductive elementelectrically couples the electrode and the electrical contact.

In one embodiment, the disclosure is directed toward a cannula thatincludes an elongated housing defining a lumen configured to allowpassage of a medical device. The cannula also includes an electrodepositioned on a distal portion of the elongated housing, an electricalcontact positioned on a proximal portion of the elongated housing, and aconductive element that resides within the elongated housing andelectrically couples the electrode to the electrical contact.

In another embodiment, the disclosure is directed toward a system thatincludes a cannula and an implant tool. The cannula includes anelongated housing defining a lumen configured to allow passage of amedical device, an electrode positioned on a distal portion of theelongated housing, a first electrical contact positioned on a proximalportion of the elongated housing, and a conductive element that resideswithin the elongated housing and electrically couples the electrode tothe electrical contact. The implant tool includes a needle coupled to ahousing and configured to be inserted into tissue of a patient and tofit within an inner lumen of the cannula and a second electrical contactconfigured to electrically couple to the first electrical contact.

In another embodiment, the disclosure is directed toward a method thatincludes introducing a cannula and needle assembly into a patient,wherein the needle is at least partially disposed within a lumen of thecannula, and wherein the lumen is configured to allow passage of amedical device. The method also includes advancing the cannula to atarget site within the patient and delivering test stimulation to thepatient via an electrode positioned at a distal portion of the cannula.

The disclosure may provide one or more advantages. For example, thecannula includes an electrode at the distal end of the cannula todeliver test stimulation to the patient before removing the needle ofthe implant tool. In this manner, the user may use the needle toreposition the cannula and again attempt to verify the target site withthe test stimulation. Utilizing test stimulation during implantation ofa medical device may reduce the time, expense, and failed treatmentassociated with inaccurate implantation of medical devices, such asleads, catheters, and microstimulators. In addition, the cannula mayhave one or more partial-ring or segmented electrodes around theperimeter of the cannula that aid the user in identifying a direction ofa target tissue site relative to the cannula. Identifying a direction ofa target tissue site within the patient may be useful, for example, todiscern a direction in which electrical stimulation may be delivered toprovide efficacious therapy.

The details of one or more embodiments of the invention are set forth inthe accompanying drawings and the description below. Other features,objects, and advantages of the invention will be apparent from thedescription and drawings, and from the claims.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a perspective view of an example stimulation therapy systemimplanted in a patient to treat a tissue site in the pelvic floor of thepatient.

FIG. 2A is a block diagram of an example implantable stimulator forproviding electrical stimulation therapy to a patient.

FIG. 2B is a block diagram of an example implantable fluid deliverydevice for providing drug delivery therapy to a patient.

FIGS. 3A and 3B are side and top views, respectively, of an exampleimplant tool having a release mechanism.

FIGS. 4A and 4B are side and bottom views, respectively, of an exampleimplant tool having a release mechanism and a cannula.

FIGS. 5A and 5B are side and front view, respectfully, of an examplerelease mechanism for an implant tool.

FIGS. 6A and 6B are side views of an example release mechanism of animplant tool.

FIGS. 7A and 7B are side and bottom views, respectfully, of an exampleimplant tool with a release mechanism having a pushing member and awheel.

FIGS. 8A and 8B are side and bottom views, respectfully, of an exampleimplant tool with a release mechanism having a pushing member and awheel to move a cannula.

FIG. 9 is an illustration of a cannula having a shape memory partiallyover a needle.

FIG. 10 is a side view of an example implantable medical lead capable ofbeing implanted via the cannula.

FIG. 11 is a block diagram of an example implantable medical devicecapable of being implanted via the cannula.

FIG. 12 is an illustration of an example implantable medical devicebeing implanted into a tissue site via the cannula.

FIGS. 13A-13D are illustrations of an example technique for implanting amedical device using an implant tool with a release mechanism.

FIG. 14 is a flow diagram of an example technique for implanting amedical device using an implant tool.

FIGS. 15A and 15B are conceptual diagrams of example cannulas having anelectrode to provide test stimulation to a patient.

FIG. 16A is a side view of an example implant tool that provides teststimulation to a patient.

FIG. 16B is a bottom view of an example implant tool having anelectrical contact to electrically connect to a cannula that deliverstest stimulation.

FIG. 17 is a flow diagram of an example technique for implanting amedical device within a patient with the aid of a cannula including oneor more electrodes for providing test stimulation to a patient.

FIG. 18 is a flow diagram of an example technique for locating a targettissue site within a patient with the aid of a cannula including one ormore electrodes for providing test stimulation to a patient.

DETAILED DESCRIPTION

Medical devices, such as medical leads or microstimulators, areimplanted within a patient at a target site to treat a patientcondition. Implant tools described herein include a needle that isintroduced into the patient and a housing coupled to the needle to allowa user to manipulate the needle position when it is at least partiallydisposed within the patient. In one embodiment, the housing includes acannula that is fitted over the needle before insertion of the needleinto the patient so that the cannula may be introduced into a patientwith the aid of the needle. Once the needle is correctly positioned atthe target site, the user withdraws the needle from the cannula, leavingthe cannula in place within the patient, such that the cannula defines aconduit that extends from outside of the patient to the target site.That is, the cannula defines an insertion path for a medical device thatextends from an entry point accessible from outside of the patient tothe target site. In this way, the cannula may also act as a “dilator”that dilates an insertion path defined by the needle in order to sizethe insertion path to receive a medical device. The user may thenimplant the desired medical device through the cannula and subsequentlyremove the cannula from the patient.

The implant tool also includes a release mechanism to facilitate theremoval of the cannula from the needle. Static friction may hinder thewithdrawal of the needle from the cannula. In such circumstances, theuser must overcome static friction between the cannula and the needle toinitiate the withdrawal of the needle from the cannula. The releasemechanism is employed to overcome the static friction and aid in theremoval of the needle without substantially changing the position of thedistal end of the cannula with respect to the target site. Inparticular, release mechanism substantially inhibits the movement of thecannula away from target tissue site. Movement of the cannula in a deepdirection toward the target tissue site (i.e., away from an entry pointinto the patient) may be inhibited by the resistance from tissue withinthe patient. The release mechanism allows the user to pull back on thehousing of the implant tool and simultaneously push the cannula forwardto ensure correct placement of the cannula. In this way, the releasemechanism aids in counteracting friction forces between the cannula andneedle that pull the cannula away from the target tissue site, where theforces are attributable to removal of the needle from the patient. Insome embodiments, the release mechanism may be activated with one hand auser, leaving the user's other hand free for other purposes, such as tohold the cannula in place in order to further prevent movement of thecannula relative to a target tissue site.

In some examples, the implant tool and cannula may facilitate locationof the tissue site for stimulation therapy. The cannula may have anelectrode located at the distal end of the cannula to deliver teststimulation to identify the desired tissue site before implanting themedical device. In this manner, the user may correctly identify thetissue site for stimulation therapy before removing the implant toolfrom the patient. For example, based on patient feedback from the teststimulation, a clinician may adjust a position of the needle and cannulawithin the patient and, in some embodiments, deliver further teststimulation to confirm placement of the needle and cannula relative tothe tissue site. The electrode of the cannula may be electricallycoupled to an electrical contact at the proximal end of the cannula viaa conductive element. In some embodiments, the conductive element islocated within the cannula, such as embedded within the cannula orotherwise coupled to the cannula. The electrical contact mayelectrically couple to an electrical contact in the housing of theimplant tool to transmit the test stimulation from the implant tool tothe cannula. In addition, the test stimulation may be generated from asignal generator within the implant tool or an external signal generatorconnected to the implant tool. These and other examples are described inmore detail below.

FIG. 1 is a prospective view of an example stimulation therapy systemimplanted in a patient to treat a tissue site in the pelvic floor of thepatient. As shown in FIG. 1, system 10 includes stimulator 14, medicallead 16, and external programmer 24. Stimulator 14 and lead 16 areimplanted within patient 12 and coupled such that stimulation 14 maydeliver stimulation therapy to the patient via lead 16. Lead 16 isimplanted through dorsal foramen 22 in sacrum 20 of patient 12 to accessa target site within the patient. The target site may be a nerve ormuscle within the pelvic floor of patient 12 to treat a variety ofdisorders. For example, system 10 may be provided to treat pelvic pain,urinary incontinence, fecal incontinence, constipation, sexualdysfunction, or other disorders. While stimulation therapy directed topelvic floor tissue of patient 12 is generally described herein,stimulation therapy of any other tissue within the patient may also beprovided. For example, system 10 may be provided for spinal cordstimulation therapy, peripheral nerve stimulation therapy, peripheralnerve field stimulation, deep brain stimulation, organ stimulation,muscle stimulation ((e.g., functional electrical stimulation (FES) ofmuscles) or any other stimulation therapy.

Stimulator 14 may provide stimulation therapy via electrical stimulationor drug delivery therapy. In the case of electrical stimulation,stimulator 14 may include a stimulation signal generator that generatesan electrical signal (e.g., pulses or substantially continuous-timesignals, such as sinusoidal signals) that is delivered to patient 12 vialead 16 that is configured to conduct the electrical signal. Lead 16 mayhave one or more electrodes positioned adjacent to a target tissue sitethat a user, e.g., a clinician or physician, desires to affect with thestimulation. Stimulator 14 generates the electrical signal according toone or more stimulation programs stored within a memory of thestimulator.

Alternatively, stimulator 14 may be configured to deliver a drug topatient 12. In the drug delivery example, stimulator 14 may store avolume of drug that is released to patient 12 in a controlled manner vialead 16. Stimulator 14 may have one or more programs that determine theamount and time for each bolus of drug for patient 12. Lead 16 may be acatheter with a lumen that allows the transfer of the drug fromstimulator 14 to the target site of patient 12. In some examples,stimulator 14 may be configured to deliver multiple types of drugs ordrugs in combination with electrical stimulation. In addition, multipleleads 16 may be implanted within patient 12 and connected to anystimulator 14.

Stimulator 14 may be programmed via communication with externalprogrammer 24. External programmer 24 may be a clinician programmer or apatient programmer that is configured to communicate wirelessly withstimulator 14. External programmer 24 may allow a user, such as patient12 or a clinician, to create stimulation programs, modify programs, viewstimulation therapy history, interrogate stimulator 14 operability, andperform other tasks related to the therapy. External programmer 24 mayinclude a user interface, processor, memory, telemetry circuit, andother components necessary for the function of the external programmer.In addition, external programmer may be embodied as a hand-held device,portable device, or a workstation, depending upon the configuration ofsystem 10.

In the embodiment shown in FIG. 1, stimulator 14 is implanted withinpatient 12 at an implant site that is close to the target site in orderto reduce the length of lead 16. In addition, the implant site forstimulator 14 may be selected to accommodate patient comfort andminimize the obtrusiveness of the implanted stimulator 14 to patientmovement and daily activities. The location in which stimulator 14resides may be, for example, a subcutaneous pocket created by aclinician and lead 16 may be tunneled through tissue from the targetsite to the pocket. In other examples, lead 16 may be coupled to a leadextension that is tunneled to stimulator 14 and coupled to thestimulator. In any case, stimulator 14 and lead 16 may be entirelyimplantable. Alternatively, stimulator 14 may be an external medicaldevice and be coupled to lead 16 which percutaneously enters thepatient. An external stimulator 14 may be useful for trial stimulationto evaluate the efficacy of chronic stimulation therapy.

As is described herein, an implant tool and cannula (not shown inFIG. 1) may be used to tunnel into patient 12 and access the target sitefor stimulation or other therapy deliver (e.g., drug delivery). Once thecannula is positioned within patient 12 by the implant tool, the cannulais used to pass lead 16 through tissue of the patient until the lead ispositioned appropriately. In some cases, lead 16 may include a fixationstructure or mechanism that secures at least the distal end of the leadin place adjacent to the target site. In any case, the implant tool mayallow a clinician to implant lead 16 into patient 12 with a minimallyinvasive technique.

FIG. 2A is a block diagram of an example implantable stimulator 14A forproviding electrical stimulation therapy to patient 12. Stimulator 14Aincludes signal generator 32, processor 28, memory 30, telemetry module36, and power source 38. In some embodiments, stimulator 14A may alsoinclude a sensing circuit (not shown in FIG. 2A) for sensing a patientparameter, such as a physiological parameter (e.g., blood pressure,temperature or electrical activity) or an activity level of patient 12.Electrodes 26A, 26B, 26C, and 26D (collectively “electrodes 26”) aredisposed on lead 16A near a distal end of the lead. The configuration,type, and number of electrodes 26 illustrated in FIG. 2A are merely anexample. In some embodiments, electrodes 26 may be ring electrodes. Inother embodiments, electrodes 26 may be segmented or partial ringelectrodes, each of which extends along an arc less than 360 degrees(e.g., 90-120 degrees) around the periphery, or circumference, of lead16A.

In embodiments in which lead 16A is a paddle lead, electrodes 26 mayextend along one side of lead 16A. Electrodes 26 extending around aportion of the circumference of lead 16A or along one side of a paddlelead may be useful for providing an electrical stimulation field in aparticular direction/targeting a particular therapy delivery site ortissue site. For example, electrodes 26 may be disposed along lead 16Asuch that the electrodes face toward nerves within the tissue site ofpatient 12, or otherwise away from the undesired tissue. In addition,the use of segmented or partial ring electrodes 26 may also reduce theoverall power delivered to electrodes 26 by stimulator 14A because ofthe efficient delivery of stimulation to the targeted nerve(s) or tissueby eliminating or minimizing the delivery of stimulation to unwanted orunnecessary regions within patient 12. Electrodes 26 of lead 16A mayalso extend along one side of lead 16A (if lead 16A includes apaddle-shaped portion) or may extend around a portion of lead 16A, asdescribed with respect to electrodes 26 of lead 16A.

In embodiments in which electrodes 26 extend around a portion of thecircumference of lead 16A or along one side of a paddle lead, lead 16Amay include one or more orientation markers (not shown) proximate to theproximal end of lead 16A that indicates the relative location ofelectrodes 26. The orientation marker may be a printed marker on lead16A, an indentation in lead 16A, a radiographic marker, or another typeof marker that is visible or otherwise detectable (e.g., detectable by aradiographic device) by a clinician. The orientation marker may help aclinician properly orient lead 16A such that electrodes 26 face thedesired direction (e.g., away from the scalp) when lead 16A is implantedwithin patient 12. For example, the orientation marker may also extendaround the same portion of the circumference of lead 16A or along theside of the paddle lead as electrodes 26. In this way, the orientationmarker faces the same direction as electrodes 26, thus indicating theorientation of electrodes 26 to the clinician. When the clinicianimplants lead 16A in the patient, the orientation marker may remainvisible to the clinician.

Stimulator 14A delivers stimulation therapy to target tissue sites viaelectrodes 26 of lead 16A. Electrodes 26 are electrically coupled to asignal generator 32 of stimulator 14A via conductors within lead 16A.More specifically, the proximal end of lead 16A includes contacts (notshown) to electrically couple electrodes 26 directly to stimulator 14Aor indirectly to stimulator 14A (e.g., via a lead extension). In oneembodiment, an implantable signal generator or other stimulationcircuitry within signal generator 32 delivers electrical signals (e.g.,pulses or substantially continuous-time signals, such as sinusoidalsignals) to target stimulation sites via at least some of electrodes 26under the control of a processor 28. Signal generator 32 may also becoupled to power source 38. Power source 38 may take the form of asmall, rechargeable or non-rechargeable battery, or an inductive powerinterface that transcutaneously receives inductively coupled energy. Inthe case of a rechargeable battery, power source 38 similarly mayinclude an inductive power interface for transcutaneous transfer ofrecharge power.

The stimulation energy generated by signal generator 32 may beformulated as stimulation energy, e.g., for treatment of any of avariety of neurological disorders, or disorders influenced by patientneurological response. The signals may be delivered from signalgenerator 32 to electrodes 26 via a switch matrix and conductors carriedby lead 16A and electrically coupled to respective electrodes 26.

Processor 28 may include a microprocessor, a controller, a digitalsignal processor (DSP), an application specific integrated circuit(ASIC), a field programmable gate array (FPGA), discrete logiccircuitry, or the like. Processor 28 controls the implantable signalgenerator within signal generator 32 to deliver stimulation therapyaccording to selected stimulation parameters. Specifically, processor 28controls signal generator 32 to deliver electrical signals with selectedamplitudes, pulse widths (if applicable), and rates specified by theprograms. In addition, processor 28 may also control signal generator 32to deliver the stimulation signals via selected subsets of electrodes 26with selected polarities. For example, electrodes 26 may be combined invarious bipolar or multi-polar combinations to deliver stimulationenergy to selected sites, such as nerve sites adjacent the spinalcolumn, pelvic floor nerve sites, cranial nerve sites, peripheral nervesites, or any other desires stimulation tissue sites.

Processor 28 may also control signal generator 32 to deliver each signalaccording to a different program, thereby interleaving programs or usingmultiple programs on each of a multiple of current sources tosimultaneously treat different symptoms or provide a combinedtherapeutic effect. For example, in addition to treatment of one symptomsuch as urinary incontinence, stimulator 14A may be configured todeliver stimulation therapy to treat other symptoms such as pelvic pain.In such an embodiment, electrodes 26 of lead 16A may be positioned todeliver stimulation therapy for treating one symptom, and electrodes 26of lead 16A may be positioned to deliver stimulation therapy fortreatment of another symptom.

Memory 30 of stimulator 14A may include any volatile or non-volatilemedia, such as a RAM, ROM, NVRAM, EEPROM, flash memory, and the like. Insome embodiments, memory 30 of stimulator 14A may store multiple sets ofstimulation parameters that are available to be selected by patient 12via external programmer 24 (FIG. 1) for delivery of stimulation therapy.For example, memory 30 may store stimulation parameters transmitted byexternal programmer 24 (FIG. 1). Memory 30 also stores programinstructions that, when executed by processor 28, cause stimulator 14Ato deliver stimulation therapy. Accordingly, computer-readable mediastoring instructions may be provided to cause processor 28 to providefunctionality as described herein.

In particular, processor 28 controls telemetry module 36 to exchangeinformation with external programmer 24, such as clinician programmerand/or a patient programmer, by wireless telemetry. In addition, in someembodiments, telemetry module 36 supports wireless communication withone or more wireless sensors that sense physiological signals andtransmit the signals to stimulator 14A.

FIG. 2B is a block diagram of an example implantable stimulator 14B forproving drug delivery therapy to patient 12. Stimulator 14B includesinfusion pump 44, processor 40, memory 42, telemetry module 46, andpower source 48. In some embodiments, stimulator 14B may also include asensing circuit (not shown in FIG. 2B). Catheter 16B, e.g., a type ofmedical lead, is a drug delivery catheter coupled to infusion pump 44 totransmit drugs from stimulator 14B to the target site of patient 12.

Stimulator 14B delivers drug delivery therapy to one or more targettissue sites within patient 16 via catheter 16B. The distal end ofcatheter 16B may include one or more holes sized for effectivetransmission of the drug to the tissue. In some examples, catheter 16Bmay include a semi-porous region at the distal end of the catheter. Inother examples, the drug may be delivered out of a very small opening atthe distal end of catheter 16B to focus the drug at one small tissuesite. In any event, infusion pump 44 includes circuitry and necessarymechanical components of a pump to release a bolus or rate of flowaccording to processor 40. Infusion pump 44 may also be coupled to powersource 48. Power source 48 may take the form of a small, rechargeable ornon-rechargeable battery, or an inductive power interface thattranscutaneously receives inductively coupled energy. In the case of arechargeable battery, power source 48 similarly may include an inductivepower interface for transcutaneous transfer of recharge power.

Processor 40 may include a microprocessor, a controller, a DSP, an ASIC,an FPGA, discrete logic circuitry, or the like. Processor 40 controlsinfusion pump 44 to deliver drug therapy according to selected therapyparameters. Specifically, processor 40 controls infusion pump 44 todeliver the drug with selected rates, bolus sizes, intervals, and otherparameters that may be used to define the delivery of drugs withinfusion pump 44

Memory 42 of stimulator 14B may include any volatile or non-volatilemedia, such as a RAM, ROM, NVRAM, EEPROM, flash memory, and the like. Insome embodiments, memory 42 of stimulator 14B may store multiple sets oftherapy parameters that are available to be selected by patient 12 viaexternal programmer 24 (FIG. 1) for delivery of stimulation therapy. Forexample, memory 42 may store stimulation parameters transmitted byexternal programmer 24 (FIG. 1). Memory 42 also stores programinstructions that, when executed by processor 40, cause stimulator 14Bto deliver stimulation drug therapy. Accordingly, computer-readablemedia storing instructions may be provided to cause processor 40 toprovide functionality as described herein.

In particular, processor 40 controls telemetry module 46 to exchangeinformation with external programmer 24, such as clinician programmerand/or a patient programmer, by wireless telemetry. In addition, in someembodiments, telemetry module 46 supports wireless communication withone or more wireless sensors that sense physiological signals andtransmit the signals to stimulator 14B.

FIGS. 3A and 3B are side and top views, respectively, of an embodimentof an implant tool including a release mechanism. As shown in FIG. 3A,implant tool 50 includes housing 52, needle 62, and release mechanism54. Needle 62 resides within a channel defined by housing 52 and haspiercing tip 64 and a shape conducive for accessing the target sitewithin patient 12 via an external tissue opening (e.g., an entry pointthrough the skin of patient 12). Release mechanism 54 is coupled tohousing 52 and includes grip 56 and guide 58 that allows a user to forcea cannula (shown in FIGS. 4A-4B) off of needle 62.

Implant tool 50 may be configured to be held in a hand of a user.Housing 52 may have a shape that is simple for constructions and/or ashape that is ergonomically formed to rest within a human hand. Housing52 may be constructed of substantial stiffness to resist flexing duringuse by the user. In addition, housing 52 defines a channel within thehousing that secures needle 62 to the housing. The channel may have twoor more segments which reside on two sides of housing 52 and, in someembodiments, engages with needle 62, to resist twisting torque appliedto needle 62 from the user. Specifically, needle 62 may form a loop thatmatches a loop-shaped channel within housing 52 that secures the needlewithin the housing. Housing 52 also defines a slot that allows releasemechanism to slide along the proximal portion of needle 62.

Housing 52 is also shaped to transmit force from the hand of the user topiercing tip 64 of needle 62. Housing 52 includes flange 60 positionedalong one side of needle 62 that supports needle 62 when the userattempts to push piercing tip 64 through tissue of patient 12 and/oradvance needle 62 through tissue. For example, when the user advancesneedle 62 through tissue of patient 12, needle 62 may contact and pushagainst a substantially rigid flange 60, which helps prevent furthermovement of needle 62. In some embodiments, flange 60 may also define asemi-circular channel that follows along the length of needle 62 todistribute any force between flange 60 and needle 62 over a greatersurface area of the needle. A space between the channel of flange 60 andneedle 62 may allow the wall of a cannula to fit between the flange andthe needle. In some examples, flange 60 may be shaped to surround agreater or lesser portion of needle 62. In other examples, flange 60 maycompletely surround needle 62 to support movements of the needle in anydirection within patient 12 when introducing the needle into tissue ofthe patient.

Release mechanism 54 includes grip 56, guide 58, and a member (notshown) connecting the grip and the guide. Release mechanism 54 isconfigured to apply force against the end of a cannula substantially ina direction toward piercing tip 64 of needle 62 or otherwise away fromhousing 52. For example, the user may press a thumb, finger or anotherobject against grip 56 to slide release mechanism 54 along needle 62. Asthe user withdraws housing 52 and needle 62 from an insertion paththrough tissue of the patient and from the cannula, the user maysubstantially simultaneously press a thumb, finger or another objectagainst grip 56, which contacts the cannula via guide 58, therebycounteracting any forces (e.g., static friction forces) that may causethe cannula that is disposed at least partially around needle 62 frombeing unintentionally withdrawn from the insertion path through alongwith needle 62. In this manner, the user may withdraw needle 62 from thecannula while keeping the cannula substantially stationary relative topatient 12 and the target tissue site. While guide 58 is shown as acylinder completely surrounding needle 62, the guide may only partiallysurround the needle in other embodiments.

Housing 52 and release mechanism 54 may be constructed of a variety ofmaterials, such as a lightweight molded plastic, e.g., polystyrene. Inother embodiments, other injection molded plastics may be used such aspolyurethane, polypropylene, high molecular weight polyurethane,polycarbonate or nylon. Alternatively, construction materials mayinclude aluminum, stainless steel, a metal alloy or a compositematerial. In addition, housing 50 and release mechanism 54 may beconstructed of different materials instead of being constructed out ofthe same material. In some examples, housing 52 and/or release mechanism54 may include a rubber or soft tactile surface to increase the frictionwith a hand of the user and prevent the hand of the user from slippingduring use. In some embodiments, housing 50 and release mechanism 54 maybe assembled through snap fit connections, adhesives or mechanicalfixation devices such as pins or screws.

Needle 62 may be constructed with a polymer or a metal. For example,needle 62 may be constructed of stainless steel, aluminum, an aluminumalloy, a titanium alloy, nitinol, or any other biocompatible material.In addition, the material used by needle 62 may be malleable (or“moldable”) by the user to create a shape capable of accessing thetarget site for stimulation. For example, a user may manipulate needle62 to define a substantially curvilinear shape to help traverse theneedle around certain anatomical features of the patient, such as anear, bones, nerves that should be avoided, and so forth. In any case,implant tool 50 may be constructed to be disposable or capable of beingsterilized after use with patient 12.

FIG. 3B shows a top view of implant tool 50. Housing 52 has a roundedshape to fit comfortably within the hand of a user. Grip 56 of releasemechanism 54 is shown near flange 60 of housing 52. Flange 60 definesslot 57, which is a substantially linear opening substantiallyconforming to the shape of needle 62. The user may push against grip 56to move release mechanism 54 toward needle 62 along slot 57 until therelease mechanism reaches the distal end 57A of the slot.

As shown in FIGS. 3A and 3B, implant tool 50 is configured so that theuser may grasp housing 52 with a hand and uses a thumb to press againstgrip 56 of release mechanism 54. In other examples, grip 56 may bepositioned at another location on housing 52 that limits the stress tothe hand of the user. For example, grip 56 may be positioned furtheraway from needle 62 or to one side of housing 52 instead of positionedalong the midline of the housing, as shown in the embodiment of FIGS.3A-3B. In any case, release mechanism 54 may slide along needle 62 topush the cannula off of the needle 62 or away from housing 52 or holdthe cannula 68 substantially in place relative to a target tissue sitewithin patient 12 as needle 62 is withdrawn from the cannula. That is,when cannula 68 is subject to resistive forces (e.g., from surroundingtissue) that inhibit movement of cannula 68, release mechanism 54essentially holds cannula 68 substantially in place as needle 62 iswithdrawn, although the force applied by release mechanism 54 to cannula58 is a pushing force away from housing 52.

FIGS. 4A and 4B are side and bottom views, respectively, of exampleimplant tool 50 including a release mechanism 54 and cannula 68. Asshown in FIG. 4A, implant tool 50 includes cannula 68 fitted over needle62 and substantially conforming to the shape of the needle. The lengthof cannula 68 is shorter than the exposed length of needle 62 to allowpiercing tip 64 to extend past the end of the cannula. In this manner,piercing tip 64 defines an insertion path for needle 62 and cannula 68through tissue of patient 12.

Cannula 68 is fitted over needle 62 and the proximal end of the cannularesides against guide 58 of release mechanism 54. In some embodiments,cannula 68 also rests against flange 60. However, in other embodiments,flange 60 does not contact cannula 68 until the user manipulates implanttool 50 such that cannula 68 flexes toward flange 60 and contacts flange60. Flange 60 transmits force from housing 52 to cannula 68 and needle62 to allow the user to push piercing tip 64 through tissue of patient12 and minimize unwanted flexing of the needle. In some examples, flange60 may resides around a greater surface area of cannula 68 to supportforces in multiple directions from the user. Once the distal end ofcannula 68 is positioned adjacent to the target site, the user pushesagainst release mechanism 54 to move the cannula off of needle 62 whilewithdrawing the needle from the cannula with housing 52. In this manner,release mechanism 54 allows the user to keep cannula 68 stationary withrespect to patient 12 while removing needle 62 from the patient. Whilethe user may use release mechanism to remove needle 62 from cannula 68with only one hand, some users may prefer to use a second hand tostabilize the cannula while removing the needle.

FIG. 4B shows the bottom view of implant tool 50. In the embodimentshown in FIG. 4B, cannula 68 resides over needle 62 and adjacent tochannel 70 defined by flange 60 and guide 58. In some embodiments,cannula 68 may fill the space between channel 70 and needle 62 in orderto transmit force from flange 60 into the needle. Guide 58 of releasemechanism 54 meets the proximal end of cannula 68 to facilitate theremoval of the cannula from needle 62. In some examples, cannula 68 mayextend into housing 52 if a longer cannula is desired for implantationof the medical device.

Cannula 68 may be constructed of a biocompatible material that isflexible to bend according to the shape of needle 62. Suitable materialsmay include polymers such as polyurethane, polyethylene, vinyl,expanded-polytetrafluoroethylene (ePTFE), or other polymers.Alternatively, cannula 68 may be constructed of a material that has ashape memory so that the cannula forms to a predetermined shape onceremoved from needle 62. Examples of suitable shape memory materialsinclude, but are not limited to, a copper-zinc-aluminium alloy,copper-aluminium-nickel alloy, a nickel-titanium alloy (e.g., Nitinol)or ethylene tetrafluoroethylene (ETFE). Cannula 68 may be constructed ofother plastics capable of being thermoset, or heated to a certain shape.Nitinol may provide an additional benefit in that it may be more readilyvisualized during fluoroscopy.

FIGS. 5A and 5B are side and front view, respectfully, of an embodimentof a release mechanism for an implant tool. As shown in FIG. 5A, releasemechanism 54 of implant tool 50 includes grip 56 and guide 58 connectedby member 72. Grip 56 is shaped with a substantially curved ramp onopposite sides of the grip to provide an ergonomic surface for engagingwith release mechanism 54. Each curved ramp meets at the top of grip 56and forms a substantially rounded apex. The bottom of grip 56 isgenerally flat; however, the bottom of the grip may be curved to matchthe curvature of housing 52 or flange 60. Member 72 is attached to thebottom of grip 56 and the top of guide 58, and shaped to providerigidity between the grip and guide. Member 72 may or may not beresistant to bending forces due to the thin dimension of the member tofit within slot 57. Member 72 is also shaped to slide within slot 57 ofhousing 52.

FIG. 5B shows a front view of release mechanism 54. Grip 56 is sized toprovide a sufficient surface area to contact the hand of the user.Member 72 has a narrow width that is sized to allow the member to slidewithin slot 57 of housing 52. In addition, guide 58 is shaped as acylinder that defines channel 74. Channel 74 is shaped and sized to fitaround the outer circumference of needle 62 such that the channel mayslide along the needle. The wall thickness T of guide 58 may besubstantially similar to the wall thickness of cannula 68 to push theend of the cannula. In some examples, guide 58 may only be semi-circularin shape such that the guide does not surround the entire needle 62.

FIG. 6A is a side view of another embodiment of a release mechanism ofan implant tool. As shown in FIG. 6A, release mechanism 74 issubstantially similar to release mechanism 54. However, releasemechanism 74 is shaped to allow grip 76 to be positioned further fromflange 60 of implant tool 50. The position of grip 76 located furtherfrom the needle of the implant tool may allow the user more leverage topush against the grip, which may be especially useful for users withsmall hands. In some examples, the position of grip 76 relative toflange 60 may be adjustable to the desires of the user.

Grip 76 is attached to guide 82 via member 80. Member 80 is elongatedand coupled to grip 76 with pivot pin 78. Pivot pin 78 allows grip 76 topivot in the plane of member 80 such that guide 82 may follow the shapeof needle 62 while the grip remains seated against housing 52. FIG. 6Bshows grip 76 that has rotated about pivot pin 78. In this manner, theshape of needle 62 does not need to follow the shape of housing 52. Inother examples, pivot pin 78 may define multiple pivot points or a balljoint to allow multiple degrees of freedom so that guide 82 may followany bend or shape of needle 62 when moving cannula 68 off of the needle.Other examples of release mechanisms may be similar to those describedherein and perform the similar function of moving cannula 68 off ofneedle 62.

FIGS. 7A and 7B are side and bottom views, respectfully, of an exampleimplant tool with a release mechanism having a pushing member and wheelassembly. Implant tool 84 is similar to implant tool 50, except thatimplant tool 84 includes a rotating release mechanism. As shown in FIG.7A, implant tool 84 includes housing 86, needle 98, and releasemechanism 89. Needle 98 resides within a channel defined by housing 86and has piercing tip 99 and a shape conducive for defining an insertionpath through tissue to access the target site within patient 12 via anexternal tissue opening, and in some embodiments, needle 98 ismalleable. Release mechanism 89 is coupled to housing 86 and includesmounts 90, wheel 92, axle 94, and pushing member 96 that allows a userto force a cannula (not shown) off of needle 98.

Implant tool 84 may be configured to be held in a hand of a user. Aswith housing 52, housing 86 may have a shape that is relatively simpleto construct and/or a shape that is ergonomically formed to rest withina human hand. Housing 86 may be constructed of substantial stiffness toresist flexing during use by the user. In addition, housing 86 defines achannel within the housing that secures needle 98 to the housing. Thechannel may have two or more segments which reside on two sides ofhousing 86 to resist twisting torque applied to needle 98 from the user.Specifically, needle 98 may form a loop that matches a loop-shapedchannel within housing 86 that secures the needle within the housing.Housing 86 also defines a slot that allows release mechanism to slidealong the proximal portion of needle 98.

Housing 86 is also shaped to transmit force from the hand of the user topiercing tip 99 of needle 98. Housing 86 includes flange 88 positionedalong one side of needle 98 that supports needle 98 when the userattempts to push piercing tip 99 through tissue of patient 12. Flange 88is substantially similar to flange 60 of implant tool 50 (FIG. 3A). Insome embodiments, flange 88 may define a semi-circular channel thatfollows along the length of needle 98 to spread out the force over agreater surface area of the needle. A space between the channel offlange 88 and needle 98 may allow the wall of a cannula to fit betweenthe flange and the needle. In some examples, flange 88 may be shaped tosurround a greater or lesser portion of needle 98. In other examples,flange 88 may completely surround needle 98 to support movements of theneedle in any direction within patient 12 when introducing the needleinto tissue of the patient.

Pushing member 96 is sized to receive needle 98, such that pushingmember 96 may be moved relative to needle 98. In one embodiment, pushingmember 96 slides along an outer surface of needle 98. Release mechanism89 includes mounts 90, wheel 92, axle 94, and pushing member 96. Releasemechanism 89 is configured to apply force against the end of a cannulain a direction substantially towards piercing tip 99 of needle 98 orotherwise away from housing 86. The user may rotate wheelcounterclockwise with a thumb or a finger to move pushing member 96along needle 98 towards piercing tip 99. In turn, the pushing member 96,which at least partially surrounds needle 98, helps initiate relativemovement between the cannula and needle 98, such as by forcing thecannula off of needle 98. In this manner, the user may withdraw needle98 from the cannula while keeping the cannula substantially stationaryrelative to patient 12. Pushing member 96 slides within a member channelwithin housing 86 and is pressed between wheel 92 and the housing sothat the friction between the wheel and the pushing member is greatenough to move the pushing member.

In some examples, wheel 92 and/or pushing member 96 may have ridges,bumps, or teeth that aid in the friction between the wheel and thepushing member. In other examples, wheel 92 may ratchet against housing86, mounts 90, or axle 94 to only allow counterclockwise movement of thewheel until the cannula is moved off of needle 98. Alternatively,pushing member 96 may ratchet within the member channel (not shown) ofhousing 86 to only allow unidirectional movement of the pushing member.The user may need to fully remove pushing member 96 from housing 86 andreinsert the pushing member into the housing to re-use the pushingmember with implant tool 84.

Housing 86 and release mechanism 89 may be constructed of a variety ofmaterials, such as a lightweight molded plastic, e.g., polystyrene. Inother embodiments, other injection molded plastics may be used such aspolyurethane, polypropylene, high molecular weight polyurethane,polycarbonate or nylon. Alternatively, construction materials mayinclude aluminum, stainless steel, a metal alloy or a compositematerial. In addition, housing 86 and release mechanism 89 may beconstructed of different materials instead of being constructed out ofthe same material. In some examples, housing 86 and/or release mechanism89 may include a rubber or soft tactile surface to prevent the hand ofthe user from slipping during use. In some embodiments, housing 86 andrelease mechanism 89 may be assembled through snap fit connections,adhesives or mechanical fixation devices such as pins or screws.

Needle 98 may be constructed with a polymer or a metal, similar toneedle 62. For example, needle 98 may be constructed of stainless steel,aluminum, an aluminum alloy, a titanium alloy, nitinol, or any otherbiocompatible material. In addition, the material used by needle 98 bemalleable by the user to create a shape capable of accessing the targetsite for stimulation. In any case, implant tool 84 may be constructed tobe disposable or capable of being sterilized after use with patient 12.

FIG. 7B shows a bottom view of implant tool 84. Housing 86 has a roundedshape to fit comfortably within the hand of a user while insertingneedle 98 into patient 12. Pushing member 96 resides within memberchannel 100 of housing 86 and exits the housing against needle 98 nearflange 88. Wheel 92 contacts pushing member 96 through an opening inhousing 86 (not shown) adjacent to the wheel, and the wheel may haveridges along the outside edge of the wheel. Wheel 92 is rotated by theuser to move pushing member 96 along needle 98 until cannula is removedfrom the needle or the pushing member can no longer be advanced by thewheel. Flange 88 also defines channel 102 that creates a space betweenthe flange and needle 98 to accept the cannula and promote the transferof force from the flange to the needle during insertion into patient 12.

As shown in FIGS. 7A and 7B, implant tool 84 is configured so that theuser grasps housing 86 with a hand and uses their thumb or finger torotate wheel 92 of release mechanism 89. In other examples, wheel 92 maybe positioned at another location on housing 86 that limits the stressto the hand of the user. For example, wheel 92 may be positioned furtheraway from needle 98 or to one side of housing 86 instead of positionedalong the midline of the housing bottom. In any case, release mechanism89 may be used to move the cannula along needle 98 and off of theneedle.

FIGS. 8A and 8B are side and bottom views, respectfully, of an exampleimplant tool with a release mechanism including a pushing member andwheel assembly to move a cannula. Cannula 104 is substantially similarto cannula 68 of FIGS. 4A and 4B. As shown in FIG. 8A, implant tool 84includes cannula 104 fitted over at least a portion of needle 98 andsubstantially conforming to the shape of the needle. The length ofcannula 104 is slightly shorter than the exposed length of needle 98 toallow piercing tip 99 to extend past the distal end of the cannula 104.In this manner, piercing tip 99 of needle 98 may define an insertionpath through tissue for needle 98 and cannula 104.

Cannula 104 is fitted over needle 98 and the proximal end of the cannularesides against pushing member 96 of release mechanism 89. Cannula 104also rests against flange 88 and is disposed between needle 98 andflange 88. Flange 88 transmits force from housing 86 to cannula 104 andneedle 98 to allow the user to apply a force to push piercing tip 99through tissue of patient 12 and minimize unwanted flexing of theneedle. In some examples, flange 88 may reside around a greater surfacearea of cannula 104 to support forces in multiple directions from theuser. Once the distal end of cannula 104 is positioned adjacent to thetarget site, the user rotates wheel 92 to move pushing member 96 againstthe cannula. In this manner, the user may initiate relative movementbetween cannula 104 and needle 98 in order to withdraw the needle fromthe cannula while substantially holding cannula 104 in place relative tothe target tissue site.

In alternative embodiments, release mechanism 89 may not require pushingmember 96 to move cannula 104 with respect to needle 98. Instead,cannula 104 may extend along needle 98 within housing 86 and bepositioned next to wheel 92. Rotation of wheel 92 may directly contactthe outside surface of cannula 104 and move the cannula along needle 98.In this manner, the user may have direct control of the release ofcannula 104 from implant tool 84.

FIG. 8A shows the bottom side of implant tool 84. Cannula 104 is shownas residing over needle 98 and adjacent to channel 102 of flange 88 andthe distal end of pushing member 96. Cannula 104 may fill the spacebetween channel 102 and needle 98 in order to transmit force from flange88 into the needle. Pushing member 96 of release mechanism 89 meets theproximal end of cannula 104 to facilitate the removal of the cannulafrom needle 98. In some examples, cannula 104 may extend to a positionwithin housing 86 if a longer cannula is needed for implantation of themedical device.

Implant tools 50 or 84 may employ alternative release mechanisms notdescribed herein but perform similar functions for substantially holdinga cannula in place proximate to a target tissue site within a patientwhile initiating relative movement between a cannula and a needle. Otherrelease mechanisms may include ratcheting mechanisms that allow the userto move the cannula in one direction and prevent the user fromretracting the cannula towards the housing. For example, the user maypush a cradle against a pushing member to force the cannula off of theneedle. The cradle may have angled teeth that lock against teeth of thepushing member when the cradle moves toward the needle. The user maythen pull the cradle back away from the needle as the teeth of thecradle and pushing member slide over each other. Additional movements ofthe cradle toward the needle may continue to move the pushing memberagainst the cannula.

FIG. 9 is an illustration of cannula 68 having a shape memory beingremoved from needle 62. While cannula 68 and implant tool 50 aredescribed in FIG. 9, other cannulas, such as cannula 104 (FIGS. 8A-8B),and implant tools, such as implant tool 84 (FIGS. 7A-8B), may be similarin function and structure. As shown in FIG. 9, as needle 62 is removedfrom lumen 106 of cannula 68, cannula 68 changes conformation to a shapeof radius R_(C). The shape may aid in directing a distal tip of amedical lead, catheter or another medical device to an appropriatetarget tissue site. In one embodiment, cannula 68 defines the shapeprior to implantation within patient 12, but adapts to the shape ofneedle 62 while needle 62 is disposed within cannula 68 because needle62 is typically more rigid than cannula 68. Upon withdrawal of needle62, cannula 68 assumes the shape defined by R_(C), which has a radius ofcurvature R_(C). R_(C) may vary due to patient anatomy or the tissuetargeted to be stimulated. In general, R_(C) is in a range ofapproximately 1 cm to 20 cm. More preferably, R_(C) is in a range ofapproximately 2 cm to 10 cm. As needle 62 is completely removed fromcannula 68, cannula 68 achieves the shape shown in FIG. 9. A medicaldevice may then be introduced into the inner lumen of cannula 68previously occupied by needle 62 of implant tool 50.

Cannula 68 may include an additional visible marker 69 to indicate thedirection in which cannula 68 is configured to curve. Marker 69 enablesthe clinician to orient implant tool 50 during implantation in thepatient such that when needle 62 is removed from the lumen of cannula68, cannula 68 curves in the desired direction. In some embodiments,marker 69 is in a location in which marker 69 remains visible to theclinician after the clinician introduces implant tool 50 into patient12. For example, marker 69 may be positioned on needle 62 in addition toor instead of on cannula 68. In general, marker 69 may be locatedanywhere on tool 50, so long as marker provides the clinician withenough information to determine which direction cannula 68 will curve.

Cannula 68 may also help refine the shape of the insertion pathpreviously defined by needle 62. In some cases, needle 62 may not beable completely define the desired insertion path because the shape(i.e., configuration) of needle 62 is dictated by the shape that isnecessary to reach the target tissue site without causing substantialdamage to tissue. For example, in some embodiments, it may be desirablefor a deep portion of the insertion path (i.e., the portion furthestfrom the entry point) to pivot or curve about 30 degrees or more.However, it may be undesirable for the distal portion of needle 62 topivot about 30 degrees or more because such a needle may be difficult toguide through tissue of the patient without causing unnecessary traumato the tissue. Cannula 68, on the other hand, may provide the pivot orcurve after being tunneled through the tissue.

The pivot or curve at the end of the insertion path may be useful forimplanting a lead, catheter or another elongated medical device to beimplanted with extra slack in order to impart strain relief to theimplanted elongated medical device. That is, upon changing shape afterthe removal of needle 62, cannula 68 may refine the insertion path toinclude a greater curvature than that achieved by needle 62, whichallows an elongated medical device to be implanted such that theelongated member has a greater length than necessary to reach theimplant site of an electrical stimulator, fluid delivery device oranother therapy device to be implanted. The greater length of theelongated medical device may help the medical device withstand pullingforces attributable to the movement of muscles along the path traversedby the elongated medical device. The shape memory aspect of cannula 68may also aid in the implantation of a medical device to regions within apatient that may be difficult to reach with needle 62, which may not beable to achieve to certain radii of curvature despite being malleable insome embodiments.

In addition to the shape memory material of cannula 68, a coating mayalso be applied to at least a part of cannula 68. For example, aparylene or oxide film coating may be applied to cannula 68 in order toelectrically insulate the cannula. Also, addition of a lubricating filmor coating, such as polytetrafluoroethylene (PTFE), to the outer surfaceof cannula 68 may be desirable to facilitate insertion.

FIG. 10 is a side view of an example implantable medical lead capable ofbeing implanted via the cannula. As shown in FIG. 10, lead 108 is anexample medical device that may be implanted using implant tool 50 andcannula 68, for example. Lead 108 includes lead body 110, tines 112, andelectrodes 114A, 114B, 114C, and 114D (collectively “electrodes 114”).Electrodes 114 may be similar to electrodes 26 of FIG. 2A. After implanttool 50 is properly positioned relative to a target site within patient12, and needle 62 is withdrawn from cannula 68, lead 108 may be advancedthrough the lumen of cannula 68 until electrodes 114 are properly placedrelative to the target site. Implant tool 50 may also be used to tunnelthe proximal end of lead 108 (not shown) to the location that stimulator14 resides patient 12.

When the user removes cannula 68 from around lead 108, tines 112 unfoldand extend into the surrounding tissue to anchor or fix the position ofelectrodes 114 relative to the target tissue site. In other examples,lead 108 may utilize less or more tines anywhere along lead housing 110.In alternative examples, lead 108 may include fixation elementsdifferent than leads 112. For example, lead 108 may incorporate any ofhelical fixation elements, snap closure elements, hydrogel elements,tissue adhesives, or sutures to anchor the lead within patient 12.

FIG. 11 is a block diagram of an example leadless medical device capableof being implanted via the cannula. Implant tool 50 or 84 and cannulas68 or 104, respectively, may also be used to directly implant a leadlesselectrical stimulation module 116 within patient 12. Stimulation module116 may be appropriate at sites where leads are not desired orstimulation is desired at multiple locations in a certain region.Stimulation module 116 may provide leadless electrical stimulation usinga unitary, integrated stimulation module carrying one or moreelectrodes, stimulation pulse generation circuitry, and optionallytelemetry circuitry. FIG. 11 is a schematic diagram illustrating anexemplary leadless electrical stimulation module 116 for electricalstimulation of a target site within patient 12. Stimulation module 116may be implanted using implant tool 50 or 84 and the respective cannula68 and 104.

Stimulation module 116 includes implantable housing 118, circuit board120, power supply 122, and electrodes 124A and 124B (collectively“electrodes 124”). Stimulation module 116 contains all necessarycomponents to provide complete stimulation therapy without any lead orother wire connected to stimulation module 116. Stimulation module 116may be implanted using devices and techniques as described in thisdisclosure.

Housing 118 is biocompatible and protects the components of stimulationmodule 116 from corrosive biological fluids and tissues. Housing 118 maycontain fixation mechanisms, such as tines similar to tines 112 of lead108 to secure stimulation module 116 near a desired nerve location.Circuit board 120 includes components such as a processor, memory,telemetry circuitry, or other electronics necessary for performingelectrical stimulation, similar to the components of stimulator 14Ashown in FIG. 2A. Power source 122 includes a battery or rechargeablebattery to power the electrical circuitry of stimulation module 116.Power source 122 may also generate power through a trickle chargerutilizing patient motion or induction with an external device.Electrodes 124 are attached to housing 118 and may be either a cathodeor anode to provide electrical stimulation. In some embodiments,stimulation module 116 may include more than two electrodes.Alternatively, electrodes 124 may be tethered to housing 116 with alead. In some embodiments, multiple leadless stimulation modules 116 maybe implanted within the pelvic floor using devices and techniques asdescribed in this disclosure.

FIG. 12 is an illustration of an example implantable medical device 116being implanted into a tissue site 126 via the cannula 68. Tissue site126 may be the pelvic floor as one example, and in other embodiments,leadless stimulation module 116 may be implanted proximate to aperipheral nerve of patient 12. A distal end 68A of cannula 68 has beenpositioned proximate to target tissue site 126 using, for example,implant tool 50. Inner lumen 106 of cannula 68 may be sized to receivemodule 116. Stimulation module 116 may be small enough to slide throughinner lumen 106 of cannula 68, such that stimulation module 116 may beimplanted proximate to target tissue site 126 within patient 12. Thatis, after distal end 68A of cannula 68 is positioned proximate to targettissue site 126 via implant tool 50 (or any other suitable implanttool), needle 62 may be withdrawn from inner lumen 106 of cannula 68.Thereafter, stimulation module 116 may be introduced into inner lumen106 of cannula 68 to reach the target tissue site 126. In otherembodiments, stimulation module 116 may be implanted through needle 62without cannula 68. In some cases, a guide wire or stylet may be used toaid in placing stimulation module 116 in an appropriate location. Inaddition, in some cases, more than one stimulation module 116 may beplaced adjacent to tissue site 126 for effective stimulation therapy.

FIGS. 13A-13D are illustrations of an example technique for implanting amedical device using an implant tool with a release mechanism. Implanttool 50 and cannula 68 will be used in the example of FIGS. 13A-13D.However, other implant tools and cannulas such as implant tool 84 andcannula 104 (shown in FIGS. 7A-8B) may be similarly used. As shown inFIG. 13A, a user begins introducing needle 62 of implant tool 50 intopatient 12 in order to implant a medical device at target site 130within the pelvic floor of the patient. As one example, target site 130may be adjacent to a sacral nerve to treat urinary incontinence. Inother embodiments, target site 130 may be any suitable tissue sitewithin patient 12, such as other nerves or muscles. Skin opening (or“entry point”) 128, through which needle 62 is inserted, may be createdby piercing tip 64 or by an incision made by the user. Skin opening 128may be just large enough for needle 62 and cannula 68 to pass intopatient 12 in order to minimize the invasiveness of the implantationprocedure.

The user holds onto housing 52 of implant tool 50 to direct theinsertion of needle 62 and cannula 68 into patient 12 via skin opening128. Generally, the path of needle 62 and cannula 68 may be controlledby the shape of needle 62. The shape of needle 62 may be preformed basedupon the implant location. Alternatively, needle 62 may be malleably,allowing the shape of needle 62 to be altered by the user during theimplantation procedure as the need arises for needle 62 to achieve adifferent shape. In this way, a malleable needle 62 enables the user topersonalize implant tool 50 the anatomy of a particular patient or to aparticular target tissue site 130. The user may guide implant tool 50along a path through tissue of patient 12 that substantially follows theshape of needle 62. In the embodiment shown in FIG. 13A, needle 62 andcannula 68 are guided through dorsal foramen 22 in sacrum 20 in order toaccess tissue site 130. In some cases, the user may use a second hand tohelp guide needle 62.

FIG. 13B shows the orientation of implant tool 50 relative to patient 12when piercing tip 64 of needle 62 is correctly placed adjacent to targetsite 130. Needle 62 and cannula 68 extend through dorsal foramen 22 insacrum 20 and out of patient 12 via skin opening 128. When removingimplant tool 50 from cannula 68, it is typically undesirable to move thecannula with respect to patient 12 and target site 130 because theposition of cannula 68 may affect the implant site for the medicaldevice, which may ultimately affect the efficacy of therapy delivery topatient 12. Thus, in order to minimize movement of cannula 68 as needle62 is withdrawn from patient 12, the user may push release mechanism 54in the direction of arrow 132 while simultaneously pulling back onimplant tool 50 in the direction of arrow 134. The user continues towithdraw implant tool 50 in the direction of arrow 134, and thedirection of withdrawal of implant tool 50 may be influenced by theshape of needle 62. By applying a force to cannula 68 that substantiallycounteracts any forces imposed on cannula 68 from the withdrawal ofimplant tool 50, release mechanism 54 retains cannula 68 substantiallyin place adjacent to target site 130 during the withdrawal of needle 62from the cannula.

FIG. 13C shows implant tool 50 partially removed from cannula 68 andpatient 12. The distal end of cannula 68 remains adjacent to target site130 while needle 62 is moved in the direction of arrow 136. Sincerelease mechanism 54 may not contact the proximal end of cannula 54during the entire removal process, the user may hold onto housing 52 ofimplant tool 50 with one hand while grasping the proximal end of cannula68 that remains outside of patient 12. In other implant techniquesutilizing other embodiments of implant tools, the release mechanism maycontinue to engage cannula 68 until needle 62 has been completelyremoved from the cannula. As previously described, however, in somecases, movement of cannula 68 relative to target tissue site 130 whenneedle 62 is withdrawn from cannula 68 may be attributable to staticfriction between cannula 68 and needle 62. Accordingly, embodiments ofimplant tools in which release mechanism 54 engages with cannula 68 tohold cannula 68 substantially in place only during an initial step ofinitiating movement between cannula 68 and needle 62 may still beuseful. After the withdrawal of implant tool 50 from cannula 68, thecannula remains within patient 12 and is ready to receive the medicaldevice for implantation through inner lumen 106.

FIG. 13D illustrates the insertion of a medical device, e.g., lead 108,into lumen 106 of cannula 68. In one embodiment, the user may graspcannula 68 with one hand and slowly advance the distal end of lead 108into the cannula in the direction of arrow 138. The user continues tofeed lead 108 into cannula 68 until electrodes 114 are correctlypositioned in relation to target site 130. In some examples the user maycouple lead 108 to a stimulator in order to deliver test stimulation totarget site 130. The test stimulation may aid the user in correctplacement of lead 108. Once lead 108 is correctly positioned, the userremoves cannula 68 while keeping lead 108 in place within patient 12.Removal of cannula 68 deploys tines 112, or other fixation devices, intosurrounding tissue, and tines 112 may expand and anchor the distal endof lead 108 adjacent to tissue site 130. In addition, the user maytunnel the proximal end of lead 108 to the location of implantablestimulator 14 using an implant tool, such as implant tool 50.

While lead 108 was implanted into patient 12 using implant tool 50 andcannula 68, other medical devices may be implanted using the techniquedescribed in FIGS. 13A-13D. For example, a microstimulator, e.g.,leadless stimulation module 116, or a fluid delivery catheter may beinserted into cannula 68 and implanted adjacent to target site 130.Alternatively, cannula 68 may be used to implant multiple leads ordevices at desired location within patient 12. In any case, the releasemechanism of the implant tool may allow the user to more easily retainthe position of the cannula adjacent to the target site.

FIG. 14 is a flow diagram of an example technique for implanting amedical device using an implant tool. Implant tool 50 and cannula 68will be used in the example of FIG. 14. However, a similar technique maybe used with implant tool 84 and cannula 104. As shown in FIG. 14, theuser begins implantation by inserting cannula 68 into patient 12 throughthe use of needle 62 of implant tool 50 (140). The user continuesinserting, or tunneling, needle 62 into patient 12 until piercing tip 64of needle 62 is positioned near the target site (142). Once the user haspositioned the distal end of cannula 68 correctly, the user uses releasemechanism 54 to begin the removal of the cannula while simultaneouslywithdrawing needle 62 from the cannula (144). A technique fordetermining whether a distal end of cannula 68 is correctly positionedrelative to a target tissue site is described below with reference toFIGS. 15-17.

The user continues to withdraw needle 62 from cannula 68 until theentire needle exits the cannula (146). With cannula in place, the userbegins to feed lead 108 through cannula 68 until electrodes 114 of thelead are placed correctly within patient 12 (148). As previouslydescribed, test electrical stimulation signals may be delivered topatient 12 via electrodes 114 of lead 108 in order to confirm placementof lead 108. In other examples, other medical devices such asstimulation module 116 may be implanted via cannula 68. The user thenremoves cannula 68 from lead 108 (150). Removal of cannula 68 from lead108 may cause fixation devices attached to the lead to deploy intosurrounding tissue, such as the extension of tines 112 that anchor thelead within patient 12. In some embodiments, the user may finishimplantation of system 10 by tunneling the proximal end of lead 108through patient 12 to an implant site for stimulator 14 and couple thelead to stimulator 14 (152). In some embodiments, additional tunnelingmay be performed by implant tool 50 and/or cannula 68.

FIGS. 15A and 15B are conceptual diagrams of example cannulas 154 and166 including one or more electrodes to provide test stimulation to apatient in order to determine a placement of the cannula 154, 156relative to a target tissue site or in order to determine a location ofthe target tissue site relative to the cannula 154, 156. Cannulas 154and 166 may be similar to cannulas 68 (FIGS. 4A-4B) and 104 (FIGS.8A-8B). However, cannulas 154 and 166 may aid the user in locating thetarget site for stimulation or other therapy delivery. As shown in FIG.15A, cannula 154 includes elongated housing 156 that defines lumen 158.

Cannula 154 also includes electrode 160 located at distal portion 156Aand electrical contact 164 located at proximal portion 156B. Electricalcontact 164 and electrode 160 are electrically coupled via conductiveelement 162 (shown in phantom lines). Test stimulation may be deliveredto patient 12 via electrode 160 of cannula 154 in order to aid the userin locating the target site for stimulation therapy or determine arelative location between distal portion 156A of cannula 154 and thetarget therapy delivery site. Electrode 160 may simulate an electrode ofa medical device implanted through cannula 154 without requiring theuser to remove the needle of an implant tool.

In addition, stimulation delivered by electrode 160 may be useful foradjusting a position of implant tool 178 (FIGS. 16A-16B) within thepatient by providing a mechanism for determining a location of thetarget site relative to electrode 160 of cannula 154. For example, upondelivering test stimulation via electrode 160 and receiving patientfeedback or observing any other patient reactions to the stimulation,the user may determine that electrode 160 is positioned a significantdistance from the target tissue site. Thus, based on informationgenerated by delivering test stimulation via electrode 160, the user mayadjust the position of implant tool 178, such as by at least partiallywithdrawing implant tool 178 and cannula 154 from the patient andreinserting the implant tool and cannula into the patient in a directionthat may be closer to the target tissue site.

Electrical contact 164 is provided on the outsider surface of cannula154 to couple to a corresponding contact of implant tool 178 (FIGS. 16Aand 16B). The coupling between the electrical contacts of cannula 154and implant tool 178 enables a stimulation signal to be transferredbetween a stimulation signal source and electrode 160. The stimulationsignal is transmitted from electrical contact 164, through conductiveelement 162, and to electrode 160 where the signal reaches tissue ofpatient 12. In other examples, electrical contact 164 may be located inlumen 158 of elongated housing 156 to couple to a contact located on theneedle of the implant tool.

In the embodiment shown in FIG. 15A, conductive element 162 is generallylocated within the material of elongated housing 156 to insulate boththe needle and surrounding tissue from the electrical signal conductedthrough the conductive element. In other embodiments, conductive element162 may be electrically insulated and disposed along an outer surface ofcannula 154 or along an inner lumen 158 of cannula 154, rather thansubstantially embedded within housing 156. Conductive element 162 may beprovided in a helical or spiral arrangement within elongated housing156. The helical shape of conductive element 162 may allow theconductive element to bend with elongated housing 156 while reducingmechanical stress to the conductive element. In other embodiments,conductive element 162 may be positioned generally straight along a sideof elongated housing 156 if cannula 154 bending may be minimal duringthe implantation procedure. In addition, cannula 154 may have multiplering, partial ring or segmented electrodes located along the length ofelongated housing 156 in addition to electrode 160, similar to lead 108.Each electrode may be coupled to separate electrical contacts viaseparate conductive elements so that a separate signal may be deliveredto each of the multiple electrodes.

Two or more electrodes on cannula 154 may be useful for, for example,providing electrodes for bipolar stimulation. If cannula 154 includes asingle electrode 160, the test electrical stimulation may be deliveredbetween electrode 160 and an external ground pad attached to an externalsurface of patient 12 or between electrode 160 and conductive needle 62(or vice versa, the stimulation may be delivered from needle 62 toelectrode 160, which acts as a ground). On the other hand, if cannula154 includes multiple electrodes, stimulation may be delivered betweenat least two of the electrodes.

As shown in FIG. 15B, another embodiment of cannula 166 includeselongated housing 168 that defines lumen 170. Cannula 166 also includeselectrodes 172A and 172B (collectively “electrodes 172) located atdistal portion 168A and electrical contacts 176A and 176B (collectively“electrical contacts 176”) located at proximal portion 168B. Electricalcontacts 176 and electrodes 172 are electrically coupled via separateconductive elements 174A and 174B (collectively “conductive elements174”).

Cannula 166 delivers test stimulation to patient 12 via at least one ofelectrodes 172 in order to aid the user in locating the target site forstimulation therapy or determining a relative position between cannula166 and the target site. Electrodes 172 may simulate an electrode of amedical device implanted through cannula 166 without requiring the userto remove the needle of an implant tool before testing the position ofthe cannula. Each of electrodes 172 are semi-circular in cross-section(e.g., partial ring or segmented electrodes) located on acircumferential subsection of the substantially cylindrical housing 168.For example, electrodes 172 may each extend around less than one-half ofthe outer circumference of elongated housing 168. In the embodimentshown in FIG. 15B, electrodes 172A and 172B have differentcircumferential positions on cannula 166.

Discrete use of one of electrodes 172 may allow the user to locate theexact location of the target site. For example, the user may deliverstimulation via one of electrodes 172 in order to determine which sideof cannula 166 the target tissue site is located. Once the user knowswhich side of cannula 166 is adjacent to the target site, the user maybe able to implant a medical device configured to direct stimulation tothat particular site or redirect implant tool 178 (FIGS. 16A-B) towardthe target site. An example medical device may be a lead with segmentedelectrodes or a complex electrode array located around the perimeter ofthe lead. This type of medical device may need to be correctly orientedin the circumferential position before insertion into cannula 166 toretain the direction information obtained from the test stimulation.

Cannula 166 may include marker 169 with which segmented or partial ringelectrodes may be aligned in order to ensure that the segmented orpartial ring electrodes are implanted in a desired orientation. Forexample, marker 169 may be aligned with one of electrodes 172A, 172B inorder to indicate the direction in which the electrode 172A or 172Bfaces. In other embodiments, cannula 166 may include more than onemarker (e.g., one marker per electrode). Marker 169 may be a printedmarker on cannula 166, an indentation in cannula 166, a radiographicmarker, or another type of marker that is visible or otherwisedetectable (e.g., detectable by a radiographic device) by a user. Inaddition, in some embodiments, marker 169 may be placed at proximalportion 168B of cannula 166 such that marker 169 remains visible to theuser when cannula 166 is partially implanted within patient 12. In otherembodiments, other types of indicator techniques may be used to identifya relative location of one or more segmented or partial ring electrodes,such as luer lock wings on cannula 166.

While effective stimulation may still be provided to patient 12 despitethe segmented electrodes of a lead not facing toward the target tissuesite, implanting the lead such that the segmented electrodes face towardthe target stimulation site may help reduce the amount of power consumedby an electrical stimulator. That is, delivering stimulation viasegmented electrodes that face toward the target stimulation site may bea more efficient use of stimulation energy because substantially thesame results may achieved with less energy as compared to deliveringstimulation via segmented electrodes facing away from the targetstimulation site.

In other examples of cannula 166, the cannula may have only onesemi-circular electrode or more than two electrodes around the perimeterof the elongated housing. In addition, some examples of cannula 166 mayinclude multiple groups of electrodes 172 along the length of distalportion 168A.

Electrical contacts 176 are provided on the outside of elongated housing168 to couple to corresponding contacts of an implant tool similar toimplant tool 178 (FIGS. 16A and 16B) to transfer the stimulation signal.The stimulation signal is transmitted from electrical contacts 176,through conductive elements 174, and to electrodes 172 where the signalreaches tissue of patient 12. In other examples, electrical contact 176may be located in lumen 170 of elongated housing 168 to couple tocontacts located on the needle of the implant tool. Alternative examplesof cannula 166 may include electrical contacts 176 embodied assemi-circular elements positioned around the perimeter of proximalportion 168B, similar to the placement of electrodes 172.

Conductive elements 174 are generally located within the material ofelongated housing 168 to insulate both the needle and surrounding tissuefrom the electrical signal conducted through the conductive elements. Inother embodiments, conductive elements 172 may be electrically insulatedand disposed along an outer surface of cannula 166 or along an innerlumen 170 of cannula 166, rather than substantially embedded withinhousing 168. Conductive elements 174 may be provided in a helical orspiral arrangement within elongated housing 168. The helical shape ofconductive element 174 may allow the conductive elements to bend withelongated housing 168 while reducing mechanical stress to the conductiveelements. In other embodiments, conductive elements 174 may bepositioned generally straight along a side of elongated housing 168 ifcannula 166 bending may be minimal during the implantation procedure.

In other embodiments, a cannula may include a single stimulationelectrode 172A or 172B that extends around less than one hundred percentof the outer perimeter of housing 168 of cannula 166. The user maydeliver stimulation to determine a direction of the target tissue siterelative to electrode 172A or 172B and rotate cannula 166 within thepatient (i.e., rotate cannula 166 along longitudinal axis 167) as neededin order to “search” in different directions for the target tissue sitewith the test stimulation. Cannula 166 is typically relatively rigid,thus, minimizing the possibility of torsion (i.e., twisting) of cannula166 when the user rotates cannula 166 while cannula 166 is disposedwithin patient 12 s.

Cannulas 154 and 166 may be constructed of a biocompatible material thatis flexible to bend according to the shape of needle 190 (FIGS. 16A and16B), similar to cannulas 68 or 104. Suitable materials may includepolymers such as polyurethane, polyethylene, vinyl,expanded-polytetrafluoroethylene (ePTFE), or other polymers.Alternatively, cannula 68 may be constructed of a material that has ashape memory so that the cannula forms to a predetermined shape onceremoved from the needle. Examples of suitable shape memory materialsinclude, but are not limited to, a copper-zinc-aluminium alloy,copper-aluminium-nickel alloy, a nickel-titanium alloy (e.g., Nitinol)or ethylene tetrafluoroethylene (ETFE). Cannula 68 may be constructed ofother plastics capable of being thermoset, or heated to a certain shape.Nitinol may provide an additional benefit in that it may be more readilyvisualized during fluoroscopy.

FIG. 16A is a side view of an example implant tool 178 that providestest stimulation to patient 12. Implant tool 178 is substantiallysimilar to implant tool 50. Cannula 154 is described in combination withimplant tool 187, but cannula 166 may also be used in some examples. Asshown in FIG. 16A, implant tool 178 includes housing 180, flange 182,release mechanism 184, grip 186, guide 188, needle 190, and cable 196.As shown in FIG. 16A, cannula 154 is fitted over needle 190 andsubstantially conforms to the shape of the needle. The length of cannula154 is slightly shorter than the exposed length of needle 190 to allowpiercing tip 192 of the needle to extend past the end of the cannula. Auser may hold implant tool 178 via housing 180 while guiding introducingneedle 190 and cannula 154 through tissue of a patient via piercing tip192.

Cannula 154 is fitted over at least a portion of needle 190 and proximalportion 156B of the cannula resides against guide 188 of releasemechanism 184. In the embodiment shown in FIG. 16A, cannula 154 alsorests against flange 182 of housing 180 and against needle 190. However,as described above, in other embodiments, cannula 154 does notnecessarily contact flange 182 until a sufficient force is applied toneedle 190 and cannula 154. Flange 182 transmits force from housing 180to cannula 154 and needle 190 to allow the user to push piercing tip 192through tissue of patient 12 and minimize unwanted flexing of theneedle. In some examples, flange 182 may resides around a greatersurface area of cannula 154 to support forces in multiple directionsfrom the user.

The user may deliver test stimulation to patient 12 via cannula 154 inorder to verify the placement of distal portion 156A of the cannularelative to a target tissue site as well as to locate a target tissuesite. In some embodiments, implant tool 178 may include a signalgenerator similar to stimulator 14A that generates a stimulation signal.Implant tool 178 may receive power via cable 196 and plug 198 when theplug is coupled to an electrical outlet. The signal generator of implanttool 178 may have predefined parameters set for test stimulation. Theuser may press button 194 to deliver the test stimulation via cannula154. Alternatively, implant tool 178 include any of a processor, memory,user interface, or telemetry circuit to program the desired teststimulation parameters into the implant tool. In other examples, implanttool 178 may be coupled to an external signal generator via cable 196and plug 198 that generates the stimulation signal for test stimulation.

The user may continue to reposition needle 190 and cannula 154 anddeliver additional test stimulations to patient 12 via electrode 160until the user verifies correct placement of distal portion 156Aadjacent to the target site. Once distal portion 156A of cannula 154 ispositioned adjacent to the target site, the user may utilize releasemechanism 184 to initiate movement between cannula 154 and needle 190.In the embodiment shown in FIG. 16A, the user may pushes against grip186 of release mechanism 184 while withdrawing the needle from thecannula with housing 180. A medical device may then be implanted withinthe patient via lumen 158 of cannula 154.

FIG. 16B shows the bottom side of implant tool 178 without a cannulaplaced over needle 190. Flange 182 defines channel 200 between theflange and needle 190. A cannula, such as cannula 154, may slide betweenwithin channel 200. Guide 188 of release mechanism 184 engages with theproximal portion of the cannula to facilitate the removal of the cannulafrom needle 190. In some examples, the cannula may extend to a positionwithin housing 180 if a longer cannula is needed for implantation of themedical device.

Implant tool 178 also includes electrical contact 202 disposed withinchannel 200 of flange 182. Electrical contact 202 is positioned tocontact electrical contact 164 of cannula 154, for example, and transmitthe test stimulation signal to the cannula. In other examples,electrical contact 202 may be disposed on needle 190, in which caseelectrical contact 164 of cannula 154 may be located within lumen 158.Alternatively, implant tool 178 may have multiple electrical contactswithin channel 200 in order to deliver test stimulation to a cannulawith any number of electrical contacts. In this manner, implant tool 178may be used with any of cannulas 154, 166 or other cannulas that includeat least one electrode.

Test stimulation may only be delivered to electrical contacts of implanttool 178 that are coupled to a cannula electrical contact that completesa circuit. Thus, if implant tool 178 is withdrawn from cannula 154, thecontact between electrical contact 202 and electrical contact 164 ofcannula 154 may be interrupted, and test stimulation may not bedelivered to patient 12 via electrode 160.

FIG. 17 is a flow diagram of an example technique for implanting amedical device within a patient with the aid of a cannula including oneor more electrodes for providing test stimulation to a patient. Implanttool 178 and cannula 154 will be used in the example of FIG. 17,although a similar technique may be used with cannula 166 (FIG. 15B). Asshown in FIG. 17, the user begins implantation by inserting cannula 154into patient 12 through the use of needle 190 of implant tool 178 (204).Piercing tip 192 of needle 190 may define an insertion path throughtissue of the patient. The user continues inserting, or tunneling,needle 190 into patient 12 until piercing tip 192 of the needle ispositioned near the target site (206).

The user delivers test stimulation with implant tool 178 to the targetsite via electrode 160 of cannula 154 (208). If the user verifies thatcannula 154 is not positioned correctly based on the feedback of patient12 or other physiological responses of patient 12 to the teststimulation (210), the user repositions piercing tip 192 of needle 190near the estimated target site (206). As previously described, ifelectrode 160 of cannula 154 is a partial ring or segmented electrode,the test stimulation delivered via electrode 160 may also be used todetermine the approximate location of the target site and readjust theposition of needle 190 and cannula 154 within patient. If the userverifies that cannula 154 is correctly positioned adjacent to the targetsite (210), the user uses release mechanism 184 to begin the removal ofthe cannula while simultaneously withdrawing needle 190 from the cannula(212).

The user continues to withdraw needle 190 from cannula 154 until theentire needle exits the cannula (214). With cannula in place within theinsertion path previously defined by the piercing tip 192 of needle 190,the user may advance lead 108 through cannula 154 until electrodes 114of the lead are placed correctly within patient 12, i.e., correctlypositioned relative to the target site (216). In other examples, othermedical devices, such as stimulation module 116 or a fluid deliverycatheter, may be implanted via cannula 154. After lead 108 is correctlypositioned relative to the target tissue site, the user may removecannula 154 from lead 108 (218). The relative position between lead 108and the target tissue site may be confirmed via test stimulationdelivered via one or more electrodes 114 of lead 108. Fixation devicesattached to the lead may deploy into tissue as cannula 154 is removedfrom patient 12. In some embodiments, the user may tunnel the proximalportion of lead 108 through patient 12 in order to couple the lead tostimulator 14 (220). In other examples, additional tunneling may beperformed by implant tool 178 and/or cannula 154.

FIG. 18 is a flow diagram of an example technique for locating a targettissue site within a patient with the aid of a cannula including one ormore electrodes for providing test stimulation to a patient. As in thetechnique shown in FIG. 17, a needle and cannula are inserted intopatient 12 (204) and test stimulation is delivered to patient 12 via atleast one of electrodes 172 of cannula 166 (206). In other embodiments,cannula 154 may be used in the technique shown in FIG. 18 if electrode160 comprises a partial ring or segmented electrode. Based on patientfeedback to the test electrical stimulation or other physiologicalresponses (e.g., a muscle contraction) to the electrical stimulation,the user may determine a location of the target tissue relative to thedirection in which stimulation was directed (222). For example, ifstimulation is delivered via electrodes 172 of cannula 166 at differenttimes, patient feedback to the stimulation via electrode 172A may becompared to the patient feedback to the stimulation via electrode 172B.The comparison may indicate whether the target tissue site is closer tostimulation electrode 172A or 172B. Any number of stimulation electrodesmay be used. If a single partial ring or segmented electrode is used todeliver the test stimulation to patient 12, the user may rotate cannula166 about longitudinal axis 167 and compare the patient response to thedifferent rotational positions of cannula 166 in order to determine theapproximate location of the target tissue relative to the cannula (222).

If the test stimulation indicates that cannula 166 is placed correctlyrelative to the target site (224), the user may user the releasemechanism 184 of implant tool 178 to initiate withdrawal of needle 190from cannula 166 (212). On the other hand, if the test stimulationindicates that cannula 166 is not placed correctly relative to thetarget site (224), the user may adjust the position of needle 190 andcannula 166 within the patient, such as by withdrawing the needle 190partially or completely from patient 12 and reinserting needle 190 intopatient 12 toward the approximate location of the target site (226).Test electrical stimulation may then be delivered via cannula 166 (208),and so forth until the user determines that cannula 166 is correctlyplaced relative to the target site (224).

Many embodiments of the invention have been described. Variousmodifications may be made without departing from the scope of theclaims. These and other embodiments are within the scope of thefollowing claims.

1. A cannula comprising: an elongated housing defining a lumenconfigured to allow passage of a medical device; an electrode positionedon a distal portion of the elongated housing; an electrical contactpositioned on a proximal portion of the elongated housing; and aconductive element that resides within the elongated housing andelectrically couples the electrode to the electrical contact.
 2. Thecannula of claim 1, wherein the elongated housing comprises a shapememory material.
 3. The cannula of claim 1, wherein the lumen defined bythe elongated housing is configured to receive a needle of an implanttool.
 4. The cannula of claim 1, wherein the electrode comprises a ringelectrode positioned around an outer circumference of the elongatedhousing.
 5. The cannula of claim 1, wherein the electrode comprises apartial ring electrode.
 6. The cannula of claim 1, further comprising aplurality of electrodes located at different circumferential positionsaround the distal end of the elongated housing.
 7. The cannula of claim6, further comprising a plurality of electrical contacts located at theproximal end of the elongated housing, wherein each of the plurality ofelectrical contacts are electrically coupled to one of the plurality ofelectrodes via separate conductive elements.
 8. The cannula of claim 1,wherein the conductive element substantially defines a helix around theelongated housing between the proximal end and the distal end.
 9. Asystem comprising: a cannula comprising: an elongated housing defining alumen configured to allow passage of a medical device; an electrodepositioned on a distal portion of the elongated housing; a firstelectrical contact positioned on a proximal portion of the elongatedhousing; and a conductive element that resides within the elongatedhousing and electrically couples the electrode to the electricalcontact; and an implant tool comprising: a needle coupled to a housingand configured to be inserted into tissue of a patient and to fit withinan inner lumen of the cannula; and a second electrical contactconfigured to electrically couple to the first electrical contact. 10.The system of claim 9, wherein the elongated housing comprises a shapememory material.
 11. The system of claim 9, wherein the electrodecomprises a ring electrode positioned around an outer circumference ofthe elongated housing.
 12. The system of claim 9, further comprising: aplurality of electrodes located at different circumferential positionsaround the distal end of the elongated housing; and a plurality ofelectrical contacts located at the proximal portion of the elongatedhousing, wherein each of the plurality of electrical contacts areelectrically coupled to one of the plurality of electrodes via separateconductive elements.
 13. The system of claim 9, further comprising asignal generator that generates test stimulation delivered to the tissuevia the electrode of the elongated housing.
 14. The system of claim 9,wherein the implant tool comprises: a flange that extends near a side ofthe needle and defines a channel configured to accept the cannulabetween the needle and the flange; and a release mechanism configured tomove the cannula toward a distal end of the needle.
 15. The system ofclaim 9, further comprising an electrical stimulator configured tocouple to the second electrical contact of the implant tool.
 16. Thesystem of claim 15, wherein the electrical stimulator is located withina housing of the implant tool.
 17. A method comprising: introducing acannula and needle assembly into a patient, wherein the needle is atleast partially disposed within a lumen of the cannula, and wherein thelumen is configured to allow passage of a medical device; advancing thecannula to a target site within the patient; and delivering teststimulation to the patient via an electrode positioned at a distalportion of the cannula.
 18. The method of claim 17, wherein advancingthe cannula comprises tunneling the cannula through tissue with apiercing tip of the needle.
 19. The method of claim 17, whereindelivering test stimulation comprises delivering test stimulation totissue of the patient located adjacent to a circumferential subsectionof the cannula.
 20. The method of claim 17, further comprising: removingthe needle from the cannula after delivering test stimulation; andpassing the medical device to the target site through the lumen of thecannula.
 21. The method of claim 20, wherein removing the needle fromthe cannula comprises: moving the cannula off of the needle in a firstdirection with a release mechanism coupled to the needle; andsimultaneously retracting the needle from the patient in a seconddirection opposite the first direction.
 22. The method of claim 17,wherein the test stimulation comprises a first test stimulation, themethod further comprising rotating the cannula and delivering a secondtest stimulation to the patient.
 23. The method of claim 17, furthercomprising adjusting a position of the needle within the patient afterdelivering the test stimulation.